Package for a retinal prosthesis

ABSTRACT

The present invention is an improved hermetic package for a retinal prosthesis implanted in the human body. The retinal prosthesis includes a flexible circuit electrode array suitable to stimulate the retina while connected to a hermetic package on the outside of the eye, the hermetic package including a cover and a base where the cover is bonded to the base such that the cover and base form the hermetic package.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/903,805, filed May 28, 2013, for Package for an ImplantableDevice, now U.S. Pat. No. 9,415,221, which is a divisional applicationof U.S. patent application Ser. No. 11/385,314, filed Mar. 20, 2006, forPackage for an Implantable Neural Stimulation Device, now U.S. Pat. No.8,473,048, which claims benefit of U.S. Provisional Patent applicationSer. No. 60/675,980, filed on Apr. 28, 2005, entitled “Implantable ChipScale Package and Low Profile Ocular Mount,” the disclosure of which isincorporated herein by reference.

This application is related to, but not dependent on, U.S. patentapplication Ser. No. 09/823,464 for Method and Apparatus for ProvidingHermetic Feedthroughs filed Mar. 30, 2001, now U.S. Pat. No. 7,480,988;Ser. No. 10/174,349 for Biocompatible Bonding Method and ElectronicsPackage Suitable for Implantation filed Jun. 17, 2002, now U.S. Pat. No.7,211,103; Ser. No. 10/236,396 for Biocompatible Bonding Method andElectronics Package Suitable for Implantation filed Sep. 6, 2002, nowU.S. Pat. No. 7,142,909; Ser. No. 10/820,240 for Retinal Prosthesis withSide Mounted Inductive Coil filed Apr. 6, 2004, now U.S. Pat. No.7,228,181; Ser. No. 11/206,482 for Package for an Implantable MedicalDevice filed Aug. 17, 2005, now U.S. Pat. No. 7,565,203; and Ser. No.11/207,644 for Flexible Circuit Electrode Array filed Aug. 19, 2005, nowU.S. Pat. No. 8,014,878, all of which are assigned to a common assigneeand incorporated herein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to retinal prostheses andmore specifically to an improved hermetic package for a retinalprosthesis.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising prostheses foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases; such as retinitispigmentosa and age related macular degeneration which affect millions ofpeople worldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, control the electronic fielddistribution and avoid undue compression of the visual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 μAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

US Patent Application 2003/0109903 to Berrang describes a Low profilesubcutaneous enclosure, in particular and metal over ceramic hermeticpackage for implantation under the skin.

SUMMARY OF THE INVENTION

The present invention is an improved hermetic package for a retinalprosthesis implanted in the human body. The retinal prosthesis includesa flexible circuit electrode array suitable to stimulate the retinawhile connected to a hermetic package on the outside of the eye, thehermetic package including a cover and a base where the cover is bondedto the base such that the cover and base form the hermetic package.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 is a side view of the implanted portion of the preferred retinalprosthesis showing the strap fan tail in more detail.

FIG. 3 is a perspective view of a partially built package showing thesubstrate, chip and the package wall.

FIG. 4 is a perspective view of the hybrid stack placed on top of thechip.

FIG. 5 is a perspective view of the partially built package showing thehybrid stack placed inside.

FIG. 6 is a perspective view of the lid to be welded to the top of thepackage.

FIG. 7 is a view of the completed package attached to an electrodearray.

FIG. 8 is a cross-section of the package.

FIG. 9 is a perspective view of the implanted portion of the preferredretinal prosthesis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

The present invention is an improved hermetic package for implantingelectronics within a body. Electronics are commonly implanted in thebody for neural stimulation and other purposes. The improved packageallows for miniaturization of the package which is particularly usefulin a retinal or other visual prosthesis for electrical stimulation ofthe retina.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. A flexible circuit 1 includes a flexiblecircuit electrode array 10 which is mounted by a retinal tack (notshown) or similar means to the epiretinal surface. The flexible circuitelectrode array 10 is electrically coupled by a flexible circuit cable12, which pierces the sclera in the pars plana region, and iselectrically coupled to an electronics package 14, external to thesclera. Further an electrode array fan tail 15 is formed of moldedsilicone and attaches the electrode array cable 12 to a molded body 18to reduce possible damage from any stresses applied during implantation.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. This is beneficial as it reduces theheight the entire device rises above the sclera. The design of theelectronic package (described below) along with a molded body 18 whichholds the secondary inductive coil 16 and electronics package 14 in theend to end orientation minimizes the thickness or height above thesclera of the entire device. This is important to minimize anyobstruction of natural eye movement.

The molded body 18 may also include suture tabs 20. The molded body 18narrows to form a strap 22 which surrounds the sclera and holds themolded body 18, secondary inductive coil 16, and electronics package 14in place. The molded body 18, suture tabs 20 and strap 22 are preferablyan integrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap 22 can better support an oval shaped secondary inductivecoil 16.

Further it is advantageous to provide a sleeve or coating 50 thatpromotes healing of the sclerotomy. Polymers such as polyimide, whichmay be used to form the flexible circuit cable 12 and flexible circuitelectrode array 10, are generally very smooth and do not promote a goodbond between the flexible circuit cable 12 and scleral tissue. A sleeveor coating of polyester, collagen, silicone, Gore-tex or similarmaterial would bond with scleral tissue and promote healing. Inparticular, a porous material will allow scleral tissue to grow into thepores promoting a good bond.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. By placing the device under the rectus muscles with theelectronics package in an area of fatty tissue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 2 shows a side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the strap fan tail 24. Whenimplanting the retinal prosthesis, it is necessary to pass the strap 22under the eye muscles to surround the sclera. The secondary inductivecoil 16 and molded body 18 must also follow the strap 22 under thelateral rectus muscle on the side of the sclera.

The implanted portion of the retinal prosthesis is very delicate. It iseasy to tear the molded body 18 or break wires in the secondaryinductive coil 16 or electrode array cable 12. In order to allow themolded body 18 to slide smoothly under the lateral rectus muscle, themolded body 18 is shaped in the form of a strap fan tail 24 on the endopposite the electronics package 14.

Referring to FIG. 3, the hermetic electronics package 14 is composed ofa ceramic substrate 60 brazed to a metal case wall 62 which is enclosedby a laser welded metal lid 84. The metal of the wall 62 and metal lid84 may be any biocompatible metal such as Titanium, niobium, platinum,iridium, palladium or combinations of such metals. The ceramic substrateis preferably alumina but may include other ceramics such as zirconia.The ceramic substrate 60 includes vias (not shown) made frombiocompatible metal and a ceramic binder using thick-film techniques.The biocompatible metal and ceramic binder is preferably platinum flakesin a ceramic paste or frit which is the ceramic used to make thesubstrate. After the vias have been filled, the substrate 60 is firedand lapped to thickness. The firing process causes the ceramic tovitrify biding the ceramic of the substrate with the ceramic of thepaste forming a hermetic bond. Thin-film metallization 66 is applied toboth the inside and outside surfaces of the ceramic substrate 60 and anASIC (Application Specific Integrated Circuit) integrated circuit chip64 is bonded to the thin film metallization on the inside of the ceramicsubstrate 60.

The inside thin film metallization 66 includes a gold layer to allowelectrical connection using wire bonding. The inside film metallizationincludes preferably two to three layers with a preferred gold top layer.The next layer to the ceramic is a titanium or tantalum or mixture oralloy thereof. The next layer is preferably palladium or platinum layeror an alloy thereof. All these metals are biocompatible. The preferredmetallization includes a titanium, palladium and gold layer. Gold is apreferred top layer because it is corrosion resistant and can be coldbonded with gold wire.

The outside thin film metallization includes a titanium adhesion layerand a platinum layer for connection to platinum electrode array traces.Platinum can be substituted by palladium or palladium/platinum alloy. Ifgold-gold wire bonding is desired a gold top layer is applied.

The package wall 62 is brazed to the ceramic substrate 60 in a vacuumfurnace using a biocompatible braze material in the braze joint.Preferably, the braze material is a nickel titanium alloy. The brazetemperature is approximately 1000° Celsius. Therefore the vias and thinfilm metallization 66 must be selected to withstand this temperature.Also, the electronics must be installed after brazing. The chip 64 isinstalled inside the package using thermocompression flip-chiptechnology. The chip is underfilled with epoxy to avoid connectionfailures due to thermal mismatch or vibration.

Referring to FIGS. 4 and 5, off-chip electrical components 70, which mayinclude capacitors, diodes, resistors or inductors (passives), areinstalled on a stack substrate 72 attached to the back of the chip 64,and connections between the stack substrate 72 and ceramic substrate 60are made using gold wire bonds 82. The stack substrate 72 is attached tothe chip 64 with non-conductive epoxy, and the passives 70 are attachedto the stack substrate 72 with conductive epoxy.

Referring to FIG. 6, the electronics package 14 is enclosed by a metallid 84 that, after a vacuum bake-out to remove volatiles and moisture,is attached using laser welding. A getter (moisture absorbent material)may be added after vacuum bake-out and before laser welding of the metallid 84. The metal lid 84 further has a metal lip 86 to protectcomponents from the welding process and further insure a good hermeticseal. The entire package is hermetically encased. Hermeticity of thevias, braze, and the entire package is verified throughout themanufacturing process. The cylindrical package was designed to have alow profile to minimize its impact on the eye when implanted.

The implant secondary inductive coil 16, which provides a means ofestablishing the inductive link between the external video processor(not shown) and the implanted device, preferably consists of gold wire.The wire is insulated with a layer of silicone. The secondary inductivecoil 16 is oval shaped. The conductive wires are wound in definedpitches and curvature shape to satisfy both the electrical functionalrequirements and the surgical constraints. The secondary inductive coil16, together with the tuning capacitors in the chip 64, forms a parallelresonant tank that is tuned at the carrier frequency to receive bothpower and data.

Referring to FIG. 7, the flexible circuit 1, includes platinumconductors 94 insulated from each other and the external environment bya biocompatible dielectric polymer 96, preferably polyimide. One end ofthe array contains exposed electrode sites that are placed in closeproximity to the retinal surface 10. The other end contains bond pads 92that permit electrical connection to the electronics package 14. Theelectronic package 14 is attached to the flexible circuit 1 using aflip-chip bumping process, and epoxy underfilled. In the flip-chipbumping process, bumps containing conductive adhesive placed on bondpads 92 and bumps containing conductive adhesive placed on theelectronic package 14 are aligned and melted to build a conductiveconnection between the bond pads 92 and the electronic package 14. Leads76 for the secondary inductive coil 16 are attached to gold pads 78 onthe ceramic substrate 60 using thermal compression bonding, and are thencovered in epoxy. The electrode array cable 12 is laser welded to theassembly junction and underfilled with epoxy. The junction of thesecondary inductive coil 16, array 1, and electronic package 14 areencapsulated with a silicone overmold 90 that connects them togethermechanically. When assembled, the hermetic electronics package 14 sitsabout 3 mm away from the end of the secondary inductive coil.

Since the implant device is implanted just under the conjunctiva it ispossible to irritate or even erode through the conjunctiva. Erodingthrough the conjunctiva leaves the body open to infection. We can doseveral things to lessen the likelihood of conjunctiva irritation orerosion. First, it is important to keep the over all thickness of theimplant to a minimum. Even though it is advantageous to mount both theelectronics package 14 and the secondary inductive coil 16 on thelateral side of the sclera, the electronics package 14 is mounted higherthan, but not covering, the secondary inductive coil 16. In other wordsthe thickness of the secondary inductive coil 16 and electronics packageshould not be cumulative.

It is also advantageous to place protective material between the implantdevice and the conjunctiva. This is particularly important at thescleratomy, where the thin film electrode array cable 12 penetrates thesclera. The thin film electrode array cable 12 must penetrate the sclerathrough the pars plana, not the retina. The scleratomy is, therefore,the point where the device comes closest to the conjunctiva. Theprotective material can be provided as a flap attached to the implantdevice or a separate piece placed by the surgeon at the time ofimplantation. Further material over the scleratomy will promote healingand sealing of the scleratomy. Suitable materials include Dacron, Teflon(polytetraflouroethylene or PTFE), Goretex (ePTFE) Tutoplast (sterilizedsclera), Mersilene (Polyester) or silicone.

Referring to FIG. 8, the package 14 contains a ceramic substrate 60,with metallized vias 65 and thin-film metallization 66. The package 14contains a metal case wall 62 which is connected to the ceramicsubstrate 60 by braze joint 61. On the ceramic substrate 60 an underfill69 is applied. On the underfill 69 an integrated circuit chip 64 ispositioned. On the integrated circuit chip 64 a ceramic hybrid substrate68 is positioned. On the ceramic hybrid substrate 68 passives 70 areplaced. Wirebonds 67 are leading from the ceramic substrate 60 to theceramic hybrid substrate 68. A metal lid 84 is connected to the metalcase wall 62 by laser welded joint 63 whereby the package 14 is sealed.

FIG. 9 shows a perspective view of the implanted portion of thepreferred retinal prosthesis which is an alternative to the retinalprosthesis shown in FIG. 1.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. The secondary inductive coil 16 is placedaround the electronics package 14 in the molded body 18. The molded body18 holds the secondary inductive coil 16 and electronics package 14 inthe end to end orientation and minimizes the thickness or height abovethe sclera of the entire device.

Accordingly, what has been shown is an improved method making a hermeticpackage for implantation in a body. While the invention has beendescribed by means of specific embodiments and applications thereof, itis understood that numerous modifications and variations could be madethereto by those skilled in the art without departing from the spiritand scope of the invention. It is therefore to be understood that withinthe scope of the claims, the invention may be practiced otherwise thanas specifically described herein.

What we claim is:
 1. A retinal prosthesis comprising: a biocompatiblepackage comprising a planar base, including an electricallynon-conductive substrate and biocompatible patterned metallizationcomprising gold on the non-conductive substrate, a circuit attacheddirectly to a first side of the base wherein the circuit is smaller thanthe base, and a rounded cover, the base and the rounded cover formingthe biocompatible package; a molded polymer body pre-curved to match thecurvature of a typical sclera and including suture tabs in the moldedpolymer body suitable to attach the biocompatible package to an outsidesurface of a sclera; and a flexible circuit electrically connected tothe circuit, the flexible circuit extending from the biocompatiblepackage and suitable to pass through a pars plana and having an array ofelectrodes suitable to stimulate retinal tissue.
 2. The retinalprosthesis according to claim 1, wherein the molded body is curved toapproximate the shape of the sclera.
 3. The retinal prosthesis accordingto claim 1, further comprising a coil receiving electrical power topower the circuit.
 4. The retinal prosthesis according to claim 1,wherein the electrically non-conductive substrate contains ceramic. 5.The retinal prosthesis according to claim 1, wherein the patternedmetallization is multiple layer metallization and the circuit is bondedto the patterned metallization.
 6. The retinal prosthesis according toclaim 5, wherein the multiple layer metallization is chosen to withstandbraze temperatures.
 7. The retinal prosthesis according to claim 6,wherein the multiple layer metallization comprises more than one of themetals titanium, tantalum, gold, palladium, platinum or layers or alloysthereof.
 8. The retinal prosthesis according to claim 1, wherein thecircuit is a flip-chip integrated circuit.
 9. The retinal prosthesisaccording to claim 1, wherein the circuit is a wire bonded circuit. 10.The retinal prosthesis according to claim 1, wherein the cover includesa wall and a lid and the wall is brazed to the base.
 11. The retinalprosthesis according to claim 1, wherein the flexible circuit is bumpbonded to the base with conductive bumps.
 12. The retinal prosthesisaccording to claim 8, further comprising a polymer underfill under theflip-chip integrated circuit.
 13. The retinal prosthesis according toclaim 11, wherein the conductive bumps contain at least one conductivepolymer.
 14. The retinal prosthesis according to claim 11, wherein theconductive bumps contain at least one conductive epoxy or polyimide. 15.The retinal prosthesis according to claim 1, further comprising agetter.
 16. The retinal prosthesis according to claim 15, wherein thegetter is placed on the inside of the cover.